Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface.

The broken linear lines in the drawing illustrate portions of the display screen or portion thereof with a graphical user interface that forms no part of the claimed design. The pixelated and/or mosaic texts, imagery, and shaded regions in the drawing illustrates portions of the display screen or portion thereof with a graphical user interface that forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 